Processes For Producing Ethanol From Acetaldehyde

ABSTRACT

In one embodiment, the invention is to a process for forming an ethanol mixture by hydrogenating an acetaldehyde feed stream in the presence of a catalyst. The acetaldehyde feed stream comprises acetaldehyde and at least one of acetic acid and ethanol. Preferably the acetaldehyde feed stream is a by-product stream from a vinyl acetate synthesis process.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation and claims priority to U.S.application Ser. No. 12/915,625, filed on Oct. 29, 2010, which is acontinuation-in-part of and claims priority to U.S. application Ser. No.12/852,269, filed on Aug. 6, 2010, which claims priority to U.S.Provisional Application No. 61/300,815, filed on Feb. 2, 2010, and U.S.Provisional Application No. 61/332,699, filed on May 7, 2010. Theseapplications are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to processes for hydrogenatingan acetaldehyde feed steam in the presence of a catalyst to form anethanol mixture.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from petrochemicalfeed stocks, such as oil, natural gas, or coal; from feed stockintermediates, such as syngas; or from starchy materials or cellulosicmaterials, such as corn or sugar cane. Conventional methods forproducing ethanol from petrochemical feed stocks, as well as fromcellulosic materials, include the acid-catalyzed hydration of ethylene,methanol homologation, direct alcohol synthesis, and Fischer-Tropschsynthesis. Instability in petrochemical feed stock prices contributes tofluctuations in the cost of conventionally produced ethanol. When feedstock prices rise, the need for alternative sources of ethanolproduction becomes more evident. Starchy materials, as well ascellulosic materials, are converted to ethanol by fermentation. However,fermentation is typically used for consumer production of ethanol forfuels or consumption. In addition, fermentation of starchy or cellulosicmaterials competes with food sources and places restraints on the amountof ethanol that can be produced for industrial use.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. During the reduction of alkanoicacid, e.g., acetic acid, other compounds are often formed with ethanolor are formed in side reactions. For example, during hydrogenation,esters are produced that together with ethanol and/or water formazeotropes, which are difficult to separate. These impurities may limitthe production of ethanol and may require expensive and complexpurification trains to separate the impurities from the ethanol. Also,the hydrogenation of acetic acid typically yields ethanol and wateralong with small amounts of side reaction-generated impurities and/orby-products. At maximum theoretical conversion and selectivity, thecrude ethanol product would comprise approximately 72 wt. % ethanol and28 wt. % water. In order to form purified ethanol, much of the waterthat is co-produced must be removed from the crude ethanol composition.In addition, when conversion is incomplete, unreacted acid may remain inthe crude ethanol product. It is typically desirable to remove thisresidual acetic acid from the crude ethanol product to yield purifiedethanol.

It is also well known to reduce, e.g., hydrogenate, aldehydes to theircorresponding alcohol. Thus, ethanol may be formed via the hydrogenationof acetaldehyde. Exemplary aldehyde hydrogenation processes aredescribed in U.S. Pat. Nos. 5,093,534; 5,004,845; 4,876,402; 4,762,817;4,626,604; 4,451,677; 4,426,541; 4,052,467; 3,953,524; and 2,549,416,the entireties of which are incorporated herein by reference.

As an example, crotonaldehyde may be hydrogenated to form crotylalcohol. The following references relate to this reaction: (1) Djerboua,et al. “On the performance of a highly loaded CO/SiO₂ catalyst in thegas phase hydrogenation of crotonaldehyde thermal treatments—catalyststructure-selectivity relationship,” Applied Catalysis A: General(2005), 282, pg 123-133; (2) Liberkova, and Tourounde, “Performance ofPt/SnO₂ catalyst in the gas phase hydrogenation of crotonaldehyde,” J.Mol. Catal. A: Chemical (2002), 180, pg. 221-230; (3) Rodrigues andBueno, “Co/SiO₂ catalysts for selective hydrogenation of crotonaldehyde:III. Promoting effect of zinc,” Applied Catalysis A: General (2004),257, pg. 210-211; (4) Ammari, et al., “An emergent catalytic material:Pt/ZnO catalyst for selective hydrogenation of crotonaldehyde,” J.Catal. (2004), 221, pg. 32-42; (5) Ammari, et al., “Selectivehydrogenation of crotonaldehyde on Pt/ZnCl₂/SiO₂ catalysts,” J. Catal.(2005), 235, pg. 1-9; (6) Consonni, et al. “High Performances of Pt/ZnOCatalysts in Selective Hydrogenation of Crotonaldehyde,” J. Catal.(1999), 188, pg. 165-175; and (7) Nitta, et al., “Selectivehydrogenation of αβ-unsaturated aldehydes on cobalt—silica catalystsobtained from cobalt chrysotile,” Applied Catal. (1989), 56, pg. 9-22.

Even in view of these teachings, the need remains for improved processesfor producing ethanol via acetaldehyde hydrogenation, which have highethanol production efficiencies.

SUMMARY OF THE INVENTION

The present invention relates to processes for producing an ethanolmixture. The process comprises the step of hydrogenating an acetaldehydefeed stream in the presence of a catalyst to form the ethanol mixture.The catalyst comprises a first metal, a silicaceous support, and atleast one support modifier. The acetaldehyde feed stream comprisesacetaldehyde and at least one of acetic acid and ethanol. Preferably,the acetaldehyde feed stream comprises from 25 wt. % to 90 wt. % ofacetaldehyde and from 10 wt. % to 75 wt. % of acetic acid and/orethanol. The ethanol mixture, as prepared by the inventive process,preferably comprises from 50 wt. % to 97 wt. % ethanol; from 0.1 wt. %to 25 wt. % water; less than 35 wt. % acetic acid; and less than 10 wt.% acetaldehyde. Preferably, the conversion of the acetaldehyde in theacetaldehyde feed stream is at least 75% and the conversion of theacetic acid in the acetaldehyde feed stream is at least 10%. Preferably,the catalyst is highly selective in converting acetaldehyde and aceticacid to ethanol. Preferably, the catalyst used in convertingacetaldehyde and/or acetic acid to ethanol provides for a selectivity toethanol of at least 80%, e.g., at least 85%, at least 88%, at least 90%,or at least 95%.

In another embodiment, the process comprises the step of contacting amixture of ethylene and acetic acid with oxygen to produce vinyl acetateand at least one by-product stream comprising acetaldehyde, e.g., from90 wt. % to 99.9 wt. % acetaldehyde. The process further comprises thestep of reacting, e.g., hydrogenating, at least a portion of the atleast one by-product stream in the presence of a catalyst to form theethanol mixture. Preferably, the at least one by-product stream isco-vaporized with a separate feed stream comprising at least one ofacetic acid and ethanol to form a vapor feed stream, which is directedto a hydrogenation reactor for hydrogenation over the catalyst to formethanol.

BRIEF DESCRIPTION OF DRAWINGS

The invention is described in detail below with reference to theappended drawings, wherein like numerals designate similar parts.

FIG. 1 is a schematic diagram of a hydrogenation system having threeseparation columns in accordance with one embodiment of the presentinvention.

FIG. 2 is a schematic diagram of a hydrogenation system having fourseparation columns in accordance with one embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Ethanol (and water) may be formed, for example, via the hydrogenation ofacetic acid as represented by the following reaction:

This reaction, however, often yields impurities and/or by-products thatare generated via side reactions. As such, significant purificationtrains may be necessary to form a purified ethanol composition. Also,the formation of these by-products reduces conversion of acetic acid toethanol.

Ethanol may also be produced via the hydrogenation of acetaldehyde. Intheoretical embodiments, ethanol is the only product of acetaldehydehydrogenation (aside from small amounts of side reaction-generatedimpurities and/or by-products). In these cases, water is not co-producedwith ethanol, as is the case in the hydrogenation of acetic acid. Thus,the resources required for removing impurities in an acetaldehydehydrogenation process may be significantly less than in an acetic acidhydrogenation process. Accordingly, in some embodiments, the processesof the present invention advantageously use the hydrogenation ofacetaldehyde to yield ethanol mixtures that contain few impurities andby-products.

In addition, without being bound by theory, the hydrogenation of aceticacid is believed to proceed through two reaction steps. The first stepis endothermic and produces acetaldehyde. The second step is thehydrogenation of the acetaldehyde to form the ethanol. This step isfaster and is exothermic. Unlike the hydrogenation of acetic acid, thehydrogenation of acetaldehyde is not believed to involve an endothermicstep. As a result, the hydrogenation of acetaldehyde, advantageously,may be carried out at a lower reactor temperature than the hydrogenationof acetic acid.

In one embodiment, the present invention is to a process for producingan ethanol mixture comprising the step of hydrogenating an acetaldehydefeed stream to produce the ethanol mixture, wherein the ethanol mixturecomprises methanol and either or both acetic acid and/or ethanol. It hasnow been discovered that the addition of acetic acid and/or ethanol tothe acetaldehyde in the feed stream surprisingly and unexpectedlyimproves hydrogenation and increases acetaldehyde conversion. Thus, inone embodiment, the acetaldehyde feed stream comprises one or moreacetaldehydes and at least one of acetic acid and ethanol. Preferably,the acetaldehyde feed stream comprises a mixture of acetaldehyde andacetic acid, a mixture of acetaldehyde and ethanol, or a mixture ofacetaldehyde, acetic acid, and ethanol. In preferred embodiments, theacetaldehyde feed stream comprises from 25 wt. % to 90 wt. %acetaldehyde, e.g., from 30 wt. % to 75 wt. % or from 40 wt. % to 60 wt.% acetaldehyde. In addition to the acetaldehyde, acetic acid, and/orethanol, the acetaldehyde feed stream may comprise additionalcomponents, such as, but not limited to, propanoic acid, water, andesters.

As indicated above, in one embodiment, the acetaldehyde feed streamcomprises acetaldehyde and acetic acid. The acetic acid may behydrogenated under the same conditions as the acetaldehyde ishydrogenated. In this embodiment, in addition to acetaldehyde, the feedstream preferably comprises less than 50 wt. % acetic acid, e.g., lessthan 45 wt. % or less than 40 wt. %. In terms of ranges, theacetaldehyde feed stream may comprise acetic acid in an amount rangingfrom 10 wt. % to 75 wt. %, e.g., from 25 wt. % to 70 wt. % or from 40wt. % to 60 wt. %.

In another embodiment, the acetaldehyde feed stream comprisesacetaldehyde and ethanol. Preferably, the ethanol passes through thereaction scheme substantially unaltered. The ethanol preferably does notsubstantially affect the hydrogenation of the acetaldehyde. When ethanolis present in the feed stream in addition to the acetaldehyde, theacetaldehyde feed stream preferably comprises less than 75 wt. %ethanol, e.g., less than 60 wt. % or less than 50 wt. %. In terms ofranges, the acetaldehyde feed stream optionally comprises ethanol in anamount ranging from 10 wt. % to 75 wt. %, e.g., from 25 wt. % to 70 wt.% or from 40 wt. % to 60 wt. %.

In one embodiment, the acetaldehyde in the acetaldehyde feed stream isobtained from a by-product stream of a vinyl acetate production process.Vinyl acetate is typically formed through the acetoxylation of ethylene.In this reaction, ethylene and acetic acid react in the presence ofoxygen to form vinyl acetate and, in some cases, by-products such asacetaldehyde. Suitable catalysts for vinyl acetate production mayinclude, for example, any of those described in GB1559540, U.S. Pat.Nos. 5,185,308; 5,691,267; 6,114,571; and 6,603,038, the disclosures ofwhich are incorporated herein by reference. In a preferred embodiment,the catalyst comprises palladium and gold, optionally on a catalystsupport. In conventional vinyl acetate synthesis processes, acetaldehydeis commonly separated from the vinyl acetate and oxidized to produceacetic acid, which is recycled to the vinyl acetate production process.In addition, acetaldehyde may be reacted with anhydrides to yieldethylidene diesters, as described in U.S. Pat. Nos. 2,859,241 and2,425,389, the disclosures of which are incorporated by reference.

In one aspect of the present invention, the acetaldehyde is recovered toform the acetaldehyde feed stream, at least a portion of which isdirected to a hydrogenation reactor for conversion to ethanol. In someembodiments of the present invention, for example, all or a portion ofthe acetaldehyde in the vinyl acetate by-product stream is hydrogenatedto form ethanol. The acetaldehyde-containing by-product stream from avinyl acetate production facility may comprise, for example, at least 95wt. % acetaldehyde, e.g., at least 97 wt. % or at least 99 wt. %acetaldehyde. In terms of ranges, the by-product stream preferablycomprises from 95 to 99.9 wt. % acetaldehyde, e.g., from 97 to 99.5 wt.% acetaldehyde. The by-product streams, may contain small amounts, e.g.,less than 1 wt. % or less than 0.1 wt. %, of impurities such asacrolein, methyl acetate, ethyl acetate, methyl formate, crotonaldehyde,propionaldehyde, propionic acid, vinyl acetate, and benzene. In terms ofranges, the by-product stream may comprise from 0.01 to 1 wt. % of eachof these components.

Preferably, the vinyl acetate by-product stream is hydrogenated in thepresence of a catalyst that is also effective for the hydrogenation ofacetic acid to form ethanol. As a result, the vinyl acetate by-productstream may be combined with acetic acid (and/or ethanol) beforehydrogenation. In these cases, the by-product stream, along with aceticacid and/or ethanol, may be vaporized before hydrogenation and theresulting vaporized feed stream is introduced into the hydrogenationreactor.

In addition to being formed as a by-product of a vinyl acetate synthesisprocess, acetaldehyde also may be formed during the hydrogenation ofacetic acid as described in U.S. Pub. No. 2010/0029993, the entirety ofwhich is incorporated herein by reference. In one embodiment, theacetaldehyde employed in the acetaldehyde feed stream is formed from thecombination of a vinyl acetate by-product stream and acetaldehydeproduced from acetic acid hydrogenation. Acetaldehyde also may be formedin the oxidation of ethylene by the Wacker process. Acetaldehyde mayalso be produced, for example, by the oxo process in which olefins arehydroformylated with carbon monoxide and hydrogen. The acetaldehydeemployed in the acetaldehyde feed stream of the invention mayalternatively be derived by any of these acetaldehyde synthesisprocesses.

In addition to the acetaldehyde, and either or both acetic acid andethanol, the acetaldehyde feed stream may further comprise one or moreother components such as carboxylic acids, anhydrides, acetone, ethylacetate, water, and mixtures thereof. In some embodiments, the presenceof carboxylic acids, such as propanoic acid or its anhydride, may bebeneficial in producing propanol.

In one embodiment, the catalyst for hydrogenating the acetaldehyde feedstream comprises a first metal, a silicaceous support, and a supportmodifier. The catalyst preferably catalyzes the hydrogenation ofacetaldehyde and, if present, acetic acid. Suitable hydrogenationcatalysts may comprise a first metal. Preferably, the catalysts may alsocomprise one or more of a second metal, a third metal, or additionalmetals. The first and optional second and third metals may be selectedfrom any Group IB, IIB, IIIB, IVB, VB, VIB, VIIB, VIII transitionalmetal, a lanthanide metal, an actinide metal or a metal selected fromany of Groups IIIA, IVA, VA, and VIA. Preferred metal combinations forsome exemplary catalyst compositions include platinum/tin,platinum/ruthenium, platinum/rhenium, palladium/ruthenium,palladium/rhenium, cobalt/palladium, cobalt/platinum, cobalt/chromium,cobalt/ruthenium, silver/palladium, copper/palladium, nickel/palladium,gold/palladium, ruthenium/rhenium, and ruthenium/iron. Exemplarycatalysts are further described in U.S. Pat. No. 7,608,744 and U.S.Publication Nos. 2010/0029995 and 2010/0197485, the entire contents anddisclosures of which are incorporated herein by reference.

In one embodiment, the first metal is selected from the group consistingof copper, iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium,iridium, platinum, titanium, zinc, chromium, rhenium, molybdenum, andtungsten. In another embodiment, the first metal is selected from thegroup consisting of platinum, palladium, cobalt, nickel, and ruthenium.Preferably, the first metal is platinum or palladium. Due to its highdemand, when the first metal comprises platinum, the catalyst preferablycomprises platinum in an amount less than 5 wt. %, e.g., less than 3 wt.%, less than 1 wt. %, or less than 0.1 wt. %.

As indicated above, the catalyst optionally further comprises a secondmetal, which may function as a promoter. If present, the second metalmay be selected from the group consisting of copper, molybdenum, tin,chromium, iron, cobalt, vanadium, tungsten, palladium, platinum,lanthanum, cerium, manganese, ruthenium, rhenium, gold, and nickel.Preferably, the second metal is selected from the group consisting ofcopper, tin, cobalt, rhenium, and nickel. More preferably, the secondmetal is tin or rhenium.

If the catalyst comprises two or more metals, e.g., a first metal and asecond metal, the first metal optionally is present in the catalyst inan amount from 0.1 to 10 wt. %, e.g., from 0.1 to 5 wt. %, or from 0.1to 3 wt. %. The second metal optionally is present in an amount from 0.1and 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to 5 wt. %. Forcatalysts comprising two or more metals, the two or more metals may bealloyed with one another or may comprise a non-alloyed metal solution ormixture.

The metal ratio may vary depending on the metals used in the catalyst.In some exemplary embodiments, the mole ratio of the first metal to thesecond metal is from 10:1 to 1:10, e.g., from 4:1 to 1:4, from 2:1 to1:2, from 1.5:1 to 1:1.5 or from 1.1:1 to 1:1.1.

The catalyst may also comprise a third metal selected from any of themetals listed above in connection with the first or second metal, solong as the third metal is different from the first and second metals.In preferred aspects, the third metal is selected from the groupconsisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin,and rhenium. More preferably, the third metal is selected from cobalt,palladium, and ruthenium. When included in the catalyst, the third metalpreferably is present in an amount from 0.05 and 4 wt. %, e.g., from 0.1to 3 wt. %, or from 0.1 to 2 wt. %.

In addition to one or more metals, the catalyst may further comprise asupport or a modified support, meaning a support that includes a supportmaterial and a support modifier, which adjusts the acidity of thesupport material. The total weight of the support or modified support,based on the total weight of the catalyst, preferably is from 75 wt. %to 99.9 wt. %, e.g., from 78 wt. % to 97 wt. %, or from 80 wt. % to 95wt. %. In preferred embodiments that use a modified support, the supportmodifier is present in an amount from 0.1 wt. % to 50 wt. %, e.g., from0.2 wt. % to 25 wt. %, from 0.5 wt. % to 15 wt. %, or from 1 wt. % to 8wt. %, based on the total weight of the catalyst.

Suitable support materials may include, for example, stable metaloxide-based supports or ceramic-based supports. Preferred supportsinclude silicaceous supports, such as silica, silica/alumina, a GroupIIA silicate such as calcium metasilicate, pyrogenic silica, high puritysilica, and mixtures thereof. Other supports may include, but are notlimited to, iron oxide, alumina, titania, zirconia, magnesium oxide,carbon, graphite, high surface area graphitized carbon, activatedcarbons, and mixtures thereof.

In some embodiments, as indicated above, the catalyst support ismodified with a support modifier. In preferred embodiments, the supportmodifier is a basic modifier that has a low volatility or no volatility.Preferably, the modifier remains on the catalyst during the reactionperiod, e.g., the modifier is not removed from the support as a resultof volatility or chromatographic effects. Thus, the modifier does notrequire in situ replacement. Such basic modifiers, for example, may beselected from the group consisting of: (i) alkaline earth oxides, (ii)alkali metal oxides, (iii) alkaline earth metal metasilicates, (iv)alkali metal metasilicates, (v) Group IIB metal oxides, (vi) Group IIBmetal metasilicates, (vii) Group IIIB metal oxides, (viii) Group IIIBmetal metasilicates, and mixtures thereof. In addition to oxides andmetasilicates, other types of modifiers including nitrates, nitrites,acetates, and lactates may be used. Preferably, the support modifier isselected from the group consisting of oxides and metasilicates of any ofsodium, potassium, magnesium, calcium, scandium, yttrium, and zinc, aswell as mixtures of any of the foregoing. Preferably, the supportmodifier is a calcium silicate, and more preferably calcium metasilicate(CaSiO₃). If the support modifier comprises calcium metasilicate, it ispreferred that at least a portion of the calcium metasilicate is incrystalline form.

A preferred silica support material is SS61138 High Surface Area (HSA)Silica Catalyst Carrier from Saint-Gobain NorPro. The Saint-GobainNorPro SS61138 silica contains approximately 95 wt. % high surface areasilica; a surface area of about 250 m²/g; a median pore diameter ofabout 12 nm; an average pore volume of about 1.0 cm³/g as measured bymercury intrusion porosimetry and a packing density of about 0.352 g/cm³(22 lb/ft³).

A preferred silica/alumina support material is KA-160 (Sud Chemie)silica spheres having a nominal diameter of about 5 mm, a density ofabout 0.562 g/ml, in absorptivity of about 0.583 g H₂O/g support, asurface area of about 160 to 175 m²/g, and a pore volume of about 0.68ml/g.

As will be appreciated by those of ordinary skill in the art, supportmaterials are selected such that the catalyst system is suitably active,selective, and robust under the process conditions employed for theformation of ethanol.

The metals of the catalysts may be dispersed throughout the support,coated on the outer surface of the support (egg shell) or decorated onthe surface of the support.

The catalyst compositions suitable for use with the present inventionpreferably are formed through metal impregnation of the modifiedsupport, although other processes such as chemical vapor deposition mayalso be employed. Such impregnation techniques are described in U.S.Pat. No. 7,608,744, U.S. Publication Nos. 2010/0029995, and2010/0197485, referred to above, the entireties of which areincorporated herein by reference.

Some embodiments of the inventive process may employ configurationsusing a fixed bed reactor and/or a fluidized bed reactor, as one ofskill in the art will readily appreciate. In many embodiments of thepresent invention, an “adiabatic” reactor can be used; that is, there islittle or no need for internal plumbing through the reaction zone to addor remove heat. In other embodiments, radial flow reactor or reactorsmay be employed, or a series of reactors may be employed with or without heat exchange, quenching, or introduction of additional feedmaterial. Alternatively, a shell and tube reactor provided with a heattransfer medium may be used. In many cases, the reaction zone may behoused in a single vessel or in a series of vessels with heat exchangerstherebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation reaction may be carried out in either the liquid phaseor vapor phase. Preferably, the reaction is carried out in the vaporphase under the following conditions. The reaction temperature may rangefrom 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225° C. to300° C., or from 250° C. to 300° C. In one embodiment when theacetaldehyde feed stream comprises acetaldehyde and ethanol, thereaction temperature may range from 125° C. to 300° C., e.g., from 150°C. to 275° C. or 175° C. to 250° C. The pressure may range from 10 KPato 3000 KPa (about 1.5 to 435 psi), e.g., from 50 KPa to 2300 KPa, orfrom 100 KPa to 1500 KPa. The reactants may be fed to the reactor at agas hourly space velocity (GHSV) of greater than 500 hr⁻¹, e.g., greaterthan 1000 hr⁻¹, greater than 2500 hr⁻¹ or even greater than 5000 hr⁻¹.In terms of ranges the GHSV may range from 50 hr⁻¹ to 50,000 hr⁻¹, e.g.,from 500 hr⁻¹ to 30,000 hr⁻¹, from 1000 hr⁻¹ to 10,000 hr⁻¹, or from1000 hr⁻¹ to 6500 hr⁻¹.

The hydrogenation optionally is carried out at a pressure justsufficient to overcome the pressure drop across the catalytic bed at theGHSV selected, although there is no bar to the use of higher pressures,it being understood that considerable pressure drop through the reactorbed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole ofacetaldehyde or acetic acid, if present, to produce one mole of ethanol,the molar ratio of hydrogen to acetaldehyde in the feed stream may rangefrom about 20:1 to 1:20, e.g., from 10:1 to 1:10, or from 8:1 to 1:8. Inone embodiment, the molar ratio of hydrogen to acetic acid may rangefrom about 20:1 to 1:20, e.g., from 10:1 to 1:10, or from 8:1 to 1:8. Inone embodiment, the molar ratio of hydrogen to acetaldehyde is greaterthan 2:1, e.g., greater than 4:1 or greater than 8:1.

In another embodiment, the molar ratio of hydrogen to acetic acid isgreater than 2:1, e.g., greater than 4:1 or greater than 8:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,of from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to30 seconds.

The raw materials of hydrogen and optionally acetic acid and/or ethanol,used in connection with the process of this invention may be derivedfrom any suitable source including natural gas, petroleum, coal,biomass, and so forth. As examples, acetic acid, if present in the feed,may be produced via methanol carbonylation, acetaldehyde oxidation,ethylene oxidation, oxidative fermentation, and anaerobic fermentation.Methanol carbonylation processes suitable for production of acetic acidare described in U.S. Pat. Nos. 7,208,624, 7,115,772, 7,005,541,6,657,078, 6,627,770, 6,143,930, 5,599,976, 5,144,068, 5,026,908,5,001,259, and 4,994,608, the disclosures of which are incorporated byreference. In one embodiment, when ethanol is present in the feed, theethanol may be obtained from the ethanol mixture produced by thehydrogenation of the acetaldehyde feed stream.

The acetaldehyde, and, if present, acetic acid, and/or ethanol, may bevaporized in a vaporizer, optionally to the reaction temperature, priorto being introduced into the hydrogenation reactor. The vaporizedacetaldehyde feed stream then may be fed along with hydrogen in anundiluted state or the vaporized acetaldehyde feed stream may be dilutedwith a relatively inert carrier gas, such as nitrogen, argon, helium,carbon dioxide and the like. For reactions run in the vapor phase, thetemperature should be controlled in the system such that it does notfall below the dew point of acetaldehyde. In one embodiment, theacetaldehyde is vaporized at the boiling point of acetaldehyde at theparticular pressure, and then the vaporized acetaldehyde is furtherheated to the reactor inlet temperature. In another embodiment theacetaldehyde is transferred to the vapor state by passing hydrogen,recycle gas, another suitable gas, or mixtures thereof through theacetaldehyde at a temperature below the boiling point of acetaldehyde,thereby humidifying the carrier gas with acetaldehyde vapors, followedby heating the mixed vapors up to the reactor inlet temperature. In oneembodiment, the acetaldehyde feed includes acetic acid in addition toacetaldehyde, and the acetic acid is vaporized at the boiling point ofacetic acid at the particular pressure, and then the vaporized aceticacid may be further heated to the reactor inlet temperature. In anotherembodiment, the acetic acid is transferred to the vapor state by passinghydrogen, recycle gas, another suitable gas, or mixtures thereof throughthe acetic acid at a temperature below the boiling point of acetic acid,thereby humidifying the carrier gas with acetic acid vapors, followed byheating the mixed vapors up to the reactor inlet temperature.Preferably, the acetaldehyde, and, if present, acetic acid and/orethanol is transferred to the vapor by passing hydrogen and/or recyclegas through the acetaldehyde, and acetic acid and/or ethanol at atemperature at or below 125° C., followed by heating of the combinedgaseous stream to the reactor inlet temperature.

In some embodiments, the hydrogenation of acetaldehyde, as well as thehydrogenation of acetic acid (if present), may achieve favorableconversion of acetaldehyde and, optionally, acetic acid and favorableselectivity and productivity to ethanol. For purposes of the presentinvention, the term “conversion” refers to the amount of a specifiedcomponent, e.g., acetaldehyde or, optionally, acetic acid, in the feedthat is converted to another compound. Conversion is expressed as a molepercentage based on the amount of acetaldehyde or acetic acid (whicheveris specified) in the feed. For acetaldehyde, the conversion preferablyis at least 75%, e.g., at least 85%, or at least 90%. If acetic acid ispresent in the feed, the acetic acid conversion may be at least 10%,e.g., at least 20%, at least 40%, at least 50%, at least 60%, at least70%, or at least 80%. Although catalysts that catalyze at highconversions, e.g., at least 80% or at least 90%, for acetaldehyde and/oracetic acid (if present) are desirable, in some embodiments a lowconversion may be acceptable where there is a high ethanol selectivity.It is within the scope of the invention to compensate for lowerconversion by using appropriate recycle streams or larger reactors. Itmay be, however, more difficult to compensate for poor selectivity.

Selectivity is expressed as a mole percent based on the specifiedconverted reactant, e.g., acetaldehyde and/or acetic acid. For example,if 30 mole % of the converted acetaldehyde is converted to ethanol, theethanol selectivity is referred to as 30%. Preferably, the selectivityof acetaldehyde and/or acetic acid to ethanol is at least 80%, e.g., atleast 85%, at least 88%, at least 90%, or at least 95%. In oneembodiment, the selectivity of acetaldehyde to ethanol is higher thanthe selectivity of acetic acid to ethanol, e.g., at least 10% higher, atleast 25% higher, or at least 50% higher. In preferred embodiments, thehydrogenation process also has a low selectivity to undesirableproducts, such as methane, ethane, and carbon dioxide. The selectivityto these undesirable products preferably is less than 4%, e.g., lessthan 2% or less than 1%. More preferably, these undesirable products arenot readily detectable in the product. In one embodiment, formation ofalkanes is low. For example, in one aspect less than 2%, less than 1%,or less than 0.5% of the acetaldehyde and/or acetic acid passed over thecatalyst may be converted to alkanes, which have little value other thanas fuel.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. A productivity of at least200 grams of ethanol per kilogram catalyst per hour, e.g., at least 400or at least 600, is preferred. In terms of ranges, the productivitypreferably is from 200 to 3,000 grams of ethanol per kilogram catalystper hour, e.g., from 400 to 2,500 or from 600 to 2,000.

In various embodiments, the crude reaction effluent, e.g., ethanolmixture, before any subsequent processing, such as purification andseparation, will typically comprise ethanol, water, and minor amounts of(unreacted)acetaldehyde, ethyl acetate, acetals, and acetone, andoptionally (unreacted) acetic acid. Exemplary embodiments of crudeethanol compositional ranges are provided in Table 1. It should beunderstood that ethanol mixture may contain other components, notlisted, such as other components in the feed.

TABLE 1 ETHANOL MIXTURES Conc. Conc. Component (wt. %) (wt. %) Conc.(wt. %) Ethanol 50 to 97 55 to 95 60 to 95 Water 0.1 to 25   1 to 25  2to 20 Acetaldehyde <10 <3 <2 Acetic Acid 10 to 95 10 to 30 15 to 25Ethyl Acetate <10 <8 <5 Acetone <5 <1 <0.1 Acetals <5 <2 <1

The amounts indicated as less than (<) in the tables throughout presentapplication are preferably not present, but if present, may be presentin trace amounts or in amounts greater than 0.0001 wt. %.

In one embodiment, the ethanol mixtures may be purified in one or moredistillation columns to remove impurities. Suitable purification systemsare described in co-pending U.S. application Ser. Nos. 12/852,227,12/852,269, and 12/833,737, the disclosures of which are incorporated byreference. Advantageously, the present invention provides a crudeethanol mixture that contains lower amounts of other products, e.g.,ethyl acetate. Thus, the resources required to separate these otherproducts from ethanol is reduced.

FIGS. 1 and 2 show a hydrogenation system 100 suitable for thehydrogenation of acetaldehyde, and optionally acetic acid, and theseparation of ethanol from the crude reaction mixture according to oneembodiment of the invention. System 100 comprises reaction zone 101 anddistillation zone 102. Reaction zone 101 comprises reactor 103, hydrogenfeed line 104, acetaldehyde feed line 105, optional acetic acid feedline 105′, and optional ethanol feed line 105″. In preferredembodiments, acetaldehyde feed line 105 is obtained from a by-productstream of a vinyl acetate production process.

In FIG. 1, distillation zone 102 comprises flasher 106, first column107, second column 108, and third column 109. In FIG. 2, distillationzone 102 further comprises a fourth column 123. Hydrogen andacetaldehyde, and optionally acetic acid and/or ethanol, are fed tovaporizer 110 via lines 104, 105, 105′ and 105″, respectively, to createa vapor feed stream in line 111. Line 111 is directed to reactor 103. Inone embodiment, lines 104 and 105 may be combined and jointly fed to thevaporizer 110, e.g., in one stream containing both hydrogen andacetaldehyde. The temperature of the vapor feed stream in line 111 ispreferably from 100° C. to 350° C., e.g., from 120° C. to 310° C. orfrom 150° C. to 300° C. Any feed that is not vaporized is removed fromvaporizer 110, as shown in FIGS. 1 and 2, and may be recycled thereto.In addition, although FIGS. 1 and 2 shows line 111 being directed to thetop of reactor 103, line 111 may be directed to the side, upper portion,or bottom of reactor 103. Further modifications and additionalcomponents to reaction zone 101 are described below.

Reactor 103 contains the catalyst that is used in the hydrogenation ofacetaldehyde. Preferably, the catalyst is also used in the hydrogenationof the carboxylic acid, e.g., acetic acid. In one embodiment, one ormore guard beds (not shown) may be used to protect the catalyst frompoisons or undesirable impurities contained in the feed orreturn/recycle streams. Such guard beds may be employed in the vapor orliquid streams. Suitable guard bed materials are known in the art andinclude, for example, carbon, silica, alumina, ceramic, or resins. Inone aspect, the guard bed media is functionalized to trap particularspecies such as sulfur or halogens. During the hydrogenation process, acrude ethanol product is withdrawn, preferably continuously, fromreactor 103 via line 112. The crude ethanol product may be condensed andfed to flasher 106, which, in turn, provides a vapor stream and a liquidstream. The flasher 106 preferably operates at a temperature of from 50°C. to 500° C., e.g., from 70° C. to 400° C. or from 100° C. to 350° C.The pressure of flasher 106 preferably is from 50 KPa to 2000 KPa, e.g.,from 75 KPa to 1500 KPa or from 100 to 1000 KPa. In one preferredembodiment the temperature and pressure of the flasher is similar to thetemperature and pressure of the reactor 103.

The vapor stream exiting the flasher 106 may comprise hydrogen andhydrocarbons, which may be purged and/or returned to reaction zone 101via line 113. As shown in FIGS. 1 and 2, the returned portion of thevapor stream passes through compressor 114 and is combined with thehydrogen feed and co-fed to vaporizer 110.

The liquid from flasher 106 is withdrawn and pumped as a feedcomposition via line 115 to the side of first column 107, also referredto as the acid separation column. The contents of line 115 typicallywill be substantially similar to the product obtained directly from thereactor, and may, in fact, also be characterized as a crude ethanolproduct. However, the feed composition in line 115 preferably hassubstantially no hydrogen, carbon dioxide, methane, or ethane, which areremoved by flasher 106. Exemplary components of liquid in line 115 areprovided in Table 2. It should be understood that liquid line 115 maycontain other components, not listed, such as components in the feed.

TABLE 2 FEED COMPOSITION Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Ethanol 50 to 97 55 to 95 60 to 95 Acetic Acid 10 to 95 10 to 30 15 to25 Water 0.1 to 25   1 to 25  2 to 20 Ethyl Acetate <10 0.001 to 8    1to 5 Acetaldehyde <10 0.001 to 3    0.1 to 3   Acetal <5 0.001 to 2   0.005 to 1    Acetone <5 0.0005 to 0.05  0.001 to 0.03  Other Esters <5<0.005 <0.001 Other Ethers <5 <0.005 <0.001 Other Alcohols <5 <0.005<0.001

The amounts indicated as less than (<) in the tables throughout presentapplication are preferably not present, but if present, may be presentin trace amounts or in amounts greater than 0.0001 wt. %.

The “other esters” in Table 2 may include, but are not limited to, ethylpropionate, methyl acetate, isopropyl acetate, n-propyl acetate, n-butylacetate or mixtures thereof. The “other ethers” in Table 2 may include,but are not limited to, diethyl ether, methyl ethyl ether, isobutylethyl ether or mixtures thereof. The “other alcohols” in Table 2 mayinclude, but are not limited to, methanol, isopropanol, n-propanol,n-butanol or mixtures thereof. In one embodiment, the feed composition,e.g., line 115, may comprise propanol, e.g., isopropanol and/orn-propanol, in an amount from 0.001 to 0.1 wt. %, from 0.001 to 0.05 wt.% or from 0.001 to 0.03 wt. %. In should be understood that these othercomponents may be carried through in any of the distillate or residuestreams described herein and will not be further described herein,unless indicated otherwise.

In embodiments where the acetaldehyde feed stream comprises acetaldehydeand ethanol, the crude reaction product preferably comprises less thanless than 5 wt. % acetic acid. Under these conditions, acid separationcolumn 107 may be skipped and line 115 may be introduced directly tosecond column 108. Second column 108 may be referred to herein as a“light ends column.” Also, in embodiments where the acetaldehyde feedstream comprises acetaldehyde and acetic acid and the conversion ofacetic acid is high, acid separation column 107 may be skipped. In thesecases, the liquid in line 116 may comprise less than 5 wt. % liquid,e.g., less than 3%.

In the embodiment shown in FIG. 1, line 115 is introduced in the lowerpart of first column 107, e.g., lower half or lower third. In apreferred embodiment, first column 107 may be used to remove unreactedacetic acid fed to the reactor 103. In these cases, the feed comprisesacetaldehyde and acetic acid. In first column 107, unreacted aceticacid, a portion of the water, and other heavy components, if present,are removed from the composition in line 115 and are withdrawn,preferably continuously, as residue. Some or all of the residue may bereturned and/or recycled back to reaction zone 101 via line 116.Although residue is shown as being co-fed with acetaldehyde in FIGS. 1and 2, residue may be directly fed to vaporizer 110 via line 116. Firstcolumn 107 also forms an overhead distillate, which is withdrawn in line117, and which may be condensed and refluxed, for example, at a ratio offrom 10:1 to 1:10, e.g., from 3:1 to 1:3 or from 1:2 to 2:1.

Any of columns 107, 108, 109, or 123 may comprise any distillationcolumn capable of separation and/or purification. The columns preferablycomprise tray columns having from 1 to 150 trays, e.g., from 10 to 100trays, from 20 to 95 trays or from 30 to 75 trays. The trays may besieve trays, fixed valve trays, movable valve trays, or any othersuitable design known in the art. In other embodiments, a packed columnmay be used. For packed columns, structured packing or random packingmay be employed. The trays or packing may be arranged in one continuouscolumn or they may be arranged in two or more columns such that thevapor from the first section enters the second section while the liquidfrom the second section enters the first section, etc.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in FIG. 1. As shown in FIG. 1,heat may be supplied to the base of each column or to a circulatingbottom stream through a heat exchanger or reboiler. Other types ofreboilers, such as internal reboilers, may also be used in someembodiments. The heat that is provided to reboilers may be derived fromany heat generated during the process that is integrated with thereboilers or from an external source such as another heat generatingchemical process or a boiler. Although one reactor and one flasher areshown in FIG. 1, additional reactors, flashers, condensers, heatingelements, and other components may be used in embodiments of the presentinvention. As will be recognized by those skilled in the art, variouscondensers, pumps, compressors, reboilers, drums, valves, connectors,separation vessels, etc., normally employed in carrying out chemicalprocesses may also be combined and employed in the processes of thepresent invention.

The temperatures and pressures employed in any of the columns may vary.As a practical matter, pressures from 10 KPa to 3000 KPa will generallybe employed in these zones although in some embodiments subatmosphericpressures may be employed as well as superatmospheric pressures.Temperatures within the various zones will normally range between theboiling points of the composition removed as the distillate and thecomposition removed as the residue. It will be recognized by thoseskilled in the art that the temperature at a given location in anoperating distillation column is dependent on the composition of thematerial at that location and the pressure of column. In addition, feedrates may vary depending on the size of the production process and, ifdescribed, may be generically referred to in terms of feed weightratios.

When column 107 is operated under standard atmospheric pressure, thetemperature of the residue exiting in line 116 from column 107preferably is from 95° C. to 120° C., e.g., from 105° C. to 117° C. orfrom 110° C. to 115° C. The temperature of the distillate exiting inline 117 from column 107 preferably is from 70° C. to 110° C., e.g.,from 75° C. to 95° C. or from 80° C. to 90° C. In other embodiments, thepressure of first column 107 may range from 0.1 KPa to 510 KPa, e.g.,from 1 KPa to 475 KPa or from 1 KPa to 375 KPa. Exemplary components ofthe distillate and residue compositions for first column 107 areprovided in Table 3 below. It should also be understood that thedistillate and residue may also contain other components, not listed,such as components in the feed. For convenience, the distillate andresidue of the first column may also be referred to as the “firstdistillate” or “first residue.” The distillates or residues of the othercolumns may also be referred to with similar numeric modifiers (second,third, etc.) in order to distinguish them from one another, but suchmodifiers should not be construed as requiring any particular separationorder.

TABLE 3 FIRST COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethanol 20 to 75 30 to 70 40 to 65 Water 10 to 40 15 to 35 20to 35 Acetic Acid <2 0.001 to 0.5  0.01 to 0.2  Ethyl Acetate <60 5.0 to40  10 to 30 Acetaldehyde <10 0.001 to 5    0.01 to 4   Acetal <0.1 <0.1<0.05 Acetone <0.05 0.001 to 0.03   0.01 to 0.025 Residue Acetic Acid 60 to 100 70 to 95 85 to 92 Water <30  1 to 20  1 to 15 Ethanol <1 <0.9<0.07

As shown in Table 3, without being bound by theory, it has surprisinglyand unexpectedly been discovered that when any amount of acetal isdetected in the feed that is introduced to the acid separation column(first column 107), the acetal appears to decompose in the column suchthat less or even no detectable amounts are present in the distillateand/or residue.

Depending on the reaction conditions, the crude ethanol product exitingreactor 103 in line 112 may comprise ethanol, acetaldehyde(unconverted), ethyl acetate, water and optionally acetic acid(unconverted). After exiting reactor 103, a non-catalyzed equilibriumreaction may occur between the components contained in the crude ethanolproduct until it is added to flasher 106 and/or first column 107. Thisequilibrium reaction tends to drive the crude ethanol product to anequilibrium between ethanol/acetic acid and ethyl acetate/water.

The distillate, e.g., overhead stream, of column 107 optionally iscondensed and refluxed as shown in FIG. 1, preferably, at a reflux ratioof 1:5 to 10:1. The distillate in line 117 preferably comprises ethanol,ethyl acetate, and water, along with other impurities, which may bedifficult to separate due to the formation of binary and tertiaryazeotropes.

The first distillate in line 117 is introduced to the second column 108,preferably in the middle part of column 108, e.g., middle half or middlethird. As one example, when a 25 tray column is used in a column withoutwater extraction, line 117 is introduced at tray 17. In one embodiment,the second column 108 may be an extractive distillation column. In suchembodiments, an extraction agent, such as water, may be added to secondcolumn 108. If the extraction agent comprises water, it may be obtainedfrom an external source or from an internal return/recycle line from oneor more of the other columns.

Second column 108 may be a tray column or packed column. In oneembodiment, second column 108 is a tray column having from 5 to 70trays, e.g., from 15 to 50 trays or from 20 to 45 trays.

Although the temperature and pressure of second column 108 may vary,when at atmospheric pressure the temperature of the second residueexiting in line 118 from second column 108 preferably is from 60° C. to90° C., e.g., from 70° C. to 90° C. or from 80° C. to 90° C. Thetemperature of the second distillate exiting in line 120 from secondcolumn 108 preferably is from 50° C. to 90° C., e.g., from 60° C. to 80°C. or from 60° C. to 70° C. Column 108 may operate at atmosphericpressure. In other embodiments, the pressure of second column 108 mayrange from 0.1 KPa to 510 KPa, e.g., from 1 KPa to 475 KPa or from 1 KPato 375 KPa. Exemplary components for the distillate and residuecompositions for second column 108 are provided in Table 4 below. Itshould be understood that the distillate and residue may also containother components, not listed, such as components in the feed.

TABLE 4 SECOND COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethyl Acetate 10 to 90 25 to 90  50 to 90 Acetaldehyde  1 to25  1 to 15  1 to 8 Water  1 to 25  1 to 20   4 to 16 Ethanol <30 0.001to 15   0.01 to 5  Acetal <5 0.001 to 2    0.01 to 1  Residue Water 30to 70 30 to 60  30 to 50 Ethanol 20 to 75 30 to 70  40 to 70 EthylAcetate <3 0.001 to 2    0.001 to 0.5 Acetic Acid <0.5 0.001 to 0.3 0.001 to 0.2

The weight ratio of ethanol in the second residue to ethanol in thesecond distillate preferably is at least 3:1, e.g., at least 6:1, atleast 8:1, at least 10:1 or at least 15:1. The weight ratio of ethylacetate in the second residue to ethyl acetate in the second distillatepreferably is less than 0.4:1, e.g., less than 0.2:1 or less than 0.1:1.In embodiments that use an extractive column with water as an extractionagent as the second column 108, the weight ratio of ethyl acetate in thesecond residue to ethyl acetate in the second distillate approacheszero.

As shown, the second residue from the bottom of second column 108, whichcomprises ethanol and water, is fed via line 118 to third column 109,also referred to as the “product column.” More preferably, the secondresidue in line 118 is introduced in the lower part of third column 109,e.g., lower half or lower third. Third column 109 recovers ethanol,which preferably is substantially pure other than the azeotropic watercontent, as the distillate in line 119. The distillate of third column109 preferably is refluxed as shown in FIG. 1, for example, at a refluxratio of from 1:10 to 10:1, e.g., from 1:3 to 3:1 or from 1:2 to 2:1.The third residue in line 121, which preferably comprises primarilywater, preferably is removed from the system 100 or may be partiallyreturned to any portion of the system 100. Third column 109 ispreferably a tray column as described above and preferably operates atatmospheric pressure. The temperature of the third distillate exiting inline 119 from third column 109 preferably is from 60° C. to 110° C.,e.g., from 70° C. to 100° C. or from 75° C. to 95° C. The temperature ofthe third residue exiting from third column 109 preferably is from 70°C. to 115° C., e.g., from 80° C. to 110° C. or from 85° C. to 105° C.,when the column is operated at atmospheric pressure. Exemplarycomponents of the distillate and residue compositions for third column109 are provided in Table 5 below. It should be understood that thedistillate and residue may also contain other components, not listed,such as components in the feed.

TABLE 5 THIRD COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethanol 75 to 96   80 to 96  85 to 96 Water <12  1 to 9  3 to8 Acetic Acid <1 0.001 to 0.1  0.005 to 0.01 Ethyl Acetate <5 0.001 to4   0.01 to 3  Residue Water 75 to 100   80 to 100   90 to 100 Ethanol<0.8 0.001 to 0.5  0.005 to 0.05 Ethyl Acetate <1 0.001 to 0.5 0.005 to0.2 Acetic Acid <2 0.001 to 0.5 0.005 to 0.2

Any of the compounds that are carried through the distillation processfrom the feed or crude reaction product generally remain in the thirddistillate in amounts of less 0.1 wt. %, based on the total weight ofthe third distillate composition, e.g., less than 0.05 wt. % or lessthan 0.02 wt. %. In one embodiment, one or more side streams may removeimpurities from any of the columns 107, 108, 109 and/or 123 in thesystem 100. Preferably at least one side stream is used to removeimpurities from the third column 109. The impurities may be purgedand/or retained within the system 100.

The third distillate in line 119 may be further purified to form ananhydrous ethanol product stream, i.e., “finished anhydrous ethanol,”using one or more additional separation systems, such as, for example,distillation columns (e.g., a finishing column) or molecular sieves.

Returning to second column 107, the second distillate preferably isrefluxed as shown in FIG. 1, for example, at a reflux ratio of from 1:10to 10:1, e.g., from 1:5 to 5:1 or from 1:3 to 3:1. In FIG. 1, the seconddistillate may be purged or recycled back to the reaction zone 101. InFIG. 2, the second distillate is fed via line 120 to fourth column 123,also referred to as the “acetaldehyde removal column.” Preferably,fourth column 123 may be used when the amount of acetaldehyde, eitherunreacted acetaldehyde or a by-product of optional acetic acidhydrogenation, is greater than 1 wt. %, e.g., greater than 3 wt. % orgreater than 5 wt. %.

In fourth column 123, the second distillate is separated into a fourthdistillate in line 124, which comprises acetaldehyde, and a fourthresidue in line 125, which comprises ethyl acetate. The fourthdistillate preferably is refluxed at a reflux ratio of from 1:20 to20:1, e.g., from 1:15 to 15:1 or from 1:10 to 10:1, and a portion of thefourth distillate is returned to the reaction zone 101. In oneembodiment, a portion of the fourth distillate is purged. For example,the fourth distillate may be combined with the acetic acid feed, ifpresent, added to the vaporizer 110, or added directly to the reactor103. In one embodiment, the fourth distillate is co-fed with theacetaldehyde in feed line 105 to vaporizer 110. Optionally, fourthdistillate may be co-fed with acetic acid feed line 105′, if present, orethanol feed line 105″.

Without being bound by theory, since the processes of the presentinvention hydrogenate acetaldehyde to form ethanol, the recycling to thereaction zone of a stream that contains acetaldehyde, e.g., stream 124,increases the yield of ethanol and decreases by-product and wastegeneration. In another embodiment (not shown), the acetaldehyde may becollected and used, with or without further purification, to make usefulproducts including but not limited to n-butanol, 1,3-butanediol, and/orcrotonaldehyde and derivatives.

The fourth residue of fourth column 123 may be purged via line 125. Thefourth residue primarily comprises ethyl acetate and ethanol, which maybe suitable for use as a solvent mixture or in the production of esters.In one preferred embodiment, the acetaldehyde is removed from the seconddistillate in fourth column 123 such that no detectable amount ofacetaldehyde is present in the residue of column 123.

Fourth column 123 is preferably a tray column as described above andpreferably operates above atmospheric pressure. The pressure of fourthcolumn 123 preferably is from 120 KPa to 5,000 KPa, e.g., from 200 KPato 4,500 KPa, or from 400 KPa to 3,000 KPa. In a preferred embodimentthe fourth column 123 may operate at a pressure that is higher than thepressure of the other columns.

The temperature of the fourth distillate exiting in line 124 from fourthcolumn 123 preferably is from 60° C. to 110° C., e.g., from 70° C. to100° C. or from 75° C. to 95° C. The temperature of the residue exitingfrom fourth column 125 preferably is from 70° C. to 115° C., e.g., from80° C. to 110° C. or from 85° C. to 110° C. Exemplary components of thedistillate and residue compositions for fourth column 123 are providedin Table 6 below. It should be understood that the distillate andresidue may also contain other components, not listed, such ascomponents in the feed.

TABLE 6 FOURTH COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Acetaldehyde 2 to 80    2 to 50 5 to 40 Ethyl Acetate <90  30 to 80 40 to 75  Ethanol <30 0.001 to 25 0.01 to 20   Water <250.001 to 20 0.01 to 15   Residue Ethyl Acetate 40 to 100    50 to 100 60to 100 Ethanol <40 0.001 to 30 0 to 15 Water <25 0.001 to 20 2 to 15Acetaldehyde  <1  0.001 to 0.5 Not detectable Acetal  <3 0.001 to 2 0.01 to 1   

The ethanol mixtures produced by the embodiments of the presentinvention may be used in a variety of applications including fuels,solvents, chemical feedstocks, pharmaceutical products, cleansers,sanitizers, hydrogenation transport or consumption. In fuelapplications, the ethanol mixtures may be blended with gasoline formotor vehicles such as automobiles, boats and small piston engineaircrafts. In non-fuel applications, the ethanol mixtures may be used asa solvent for toiletry and cosmetic preparations, detergents,disinfectants, coatings, inks, and pharmaceuticals. The ethanol mixturesmay also be used as a processing solvent in manufacturing processes formedicinal products, food preparations, dyes, photochemicals and latexprocessing.

The ethanol mixtures may also be used a chemical feedstock to make otherchemicals such as vinegar, ethyl acrylate, ethyl acetate, ethylene,glycol ethers, ethylamines, aldehydes, and higher alcohols, especiallybutanol. In the production of ethyl acetate, the ethanol mixtures may beesterified with acetic acid or reacted with polyvinyl acetate. Theethanol mixtures may be dehydrated to produce ethylene. Any of knowndehydration catalysts can be employed in to dehydrate ethanol, such asthose described in copending U.S. Pub. Nos. 2010/0030002 and2010/0030001, the disclosures of which are incorporated by reference. Azeolite catalyst, for example, may be employed as the dehydrationcatalyst. Preferably, the zeolite has a pore diameter of at least about0.6 nm, and preferred zeolites include dehydration catalysts selectedfrom the group consisting of mordenites, ZSM-5, a zeolite X and azeolite Y. Zeolite X is described, for example, in U.S. Pat. No.2,882,244 and zeolite Y in U.S. Pat. No. 3,130,007, the disclosures ofwhich are incorporated by reference.

The invention is described in detail below with reference to numerousembodiments for purposes of exemplification and illustration only.Modifications to particular embodiments within the spirit and scope ofthe present invention, set forth in the appended claims, will be readilyapparent to those of skill in the art.

The following examples describe the procedures used for the preparationof various catalysts employed in the process of this invention.

EXAMPLES Example 1

An acetaldehyde feed stream comprising 50 wt. % acetaldehyde and 50 wt.% acetic acid was hydrogenated in the presence of a catalyst comprising1.6 wt. % platinum and 1 wt. % tin supported on ⅛ inch calcium silicatemodified silica extrudates. The hydrogenation reaction was performed inthe vapor phase at a temperature of 250° C., a pressure of 250 psig, andat a GHSV of 4,500 hr⁻¹. The composition of the crude ethanol mixture inthe reactor effluent is provided in Table 7 below.

Example 2

The acetaldehyde feed stream was hydrogenated as in Example 1, but at atemperature of 300° C. The composition of the crude resultant ethanolmixture in the reactor effluent is provided in Table 7.

Example 3

An acetaldehyde feed stream having 50 wt. % acetaldehyde and 50 wt. %ethanol was hydrogenated under the conditions described in Example 1.The composition of the crude resultant ethanol mixture in the reactoreffluent is provided in Table 7.

Example 4

The acetaldehyde feed stream was hydrogenation as in Example 3, but at atemperature of 300° C. The composition of the crude resultant ethanolmixture in the reactor effluent is provided in Table 7.

TABLE 7 Example 1 2 3 4 Feed Stream Acetaldehyde   50 wt. %   50 wt. %50 wt. % 50 wt. % Acetic Acid   50 wt. %   50 wt. % — — Ethanol — — 50wt. % 50 wt. % Hydrogenation 250° C. 300° C. 250° C. 300° C. Temp.Reactor Effluent Ethanol 64.7 wt. % 71.1 wt. % 96.1%  90.4%  Water  7.5wt. % 12.5 wt. % 0.5% 1.3% Acetic Acid 24.2 wt. % 11.5 wt. % 0.6% 0.9%Acetaldehyde  0.2 wt. %  1.4 wt. % 0.6% 1.4% Acetone 0.01 wt. %  0.0 wt.% 0.01%  0.1% Acetal  1.7 wt. %  1.8 wt. % 0.3% 0.6% Ethyl Acetate  4.9wt. %  6.4 wt. % 1.1% 2.8% Acetaldehyde 99.6% 97.2% 98.9%   97%Conversion Acetic Acid 51.5% 76.8% — — Conversion

For the acetaldehyde/acetic acid feed stream of Examples 1 and 2, theyield of ethanol was greater at the higher temperature. For theacetaldehyde/ethanol feed stream of Examples 3 and 4, the yield ofethanol was greater at the lower temperature. The conversion ofacetaldehyde to ethanol is an exothermic reaction and lower reactiontemperatures are more beneficial. The conversion of acetic acid toethanol is believed to involve at least two steps. The first step is theconversion of acetic acid to acetaldehyde, which is endothermic. Thesecond step is the conversion of acetaldehyde to ethanol. The first stepis slower than the second step. Also, the first step also yields wateras a co-product.

In each of the examples, the conversion of acetaldehyde to ethanol wasgreater than 96%.

For Examples 3 and 4, the feed stream started with 50 wt. % of ethanol.This ethanol is believed to proceed through the reaction essentiallyunaltered during the hydrogenation.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In view of the foregoing discussion, relevantknowledge in the art and references discussed above in connection withthe Background and Detailed Description, the disclosures of which areall incorporated herein by reference. In addition, it should beunderstood that aspects of the invention and portions of variousembodiments and various features recited below and/or in the appendedclaims may be combined or interchanged either in whole or in part. Inthe foregoing descriptions of the various embodiments, those embodimentswhich refer to another embodiment may be appropriately combined withother embodiments as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

1-20. (canceled)
 21. A process for producing an ethanol mixture,comprising the steps of: hydrogenating a feed stream that comprises 25wt. % to 90 wt. % acetaldehyde and from 10 wt. % to 75 wt. % acetic acidin a reactor in the presence of a catalyst to form the ethanol mixturethat comprises ethanol and acetaldehyde, wherein the catalyst comprisesa first metal, a support, and at least one support modifier; separatingacetaldehyde from the ethanol mixture; feeding the separatedacetaldehyde to the reactor; and recovering ethanol from the ethanolmixture.
 22. The process of claim 21, wherein the feed stream comprisesless than 50 wt. % acetic acid.
 23. The process of claim 21, furthercomprising: vaporizing the feed stream to form a vapor feed stream; andreacting the vapor feed stream in the presence of the catalyst.
 24. Theprocess of claim 21, wherein the hydrogenation is performed at atemperature of from 125° C. to 350° C.
 25. The process of claim 21,wherein the hydrogenation is performed at a pressure of 10 kPa to 3000kPa.
 26. The process of claim 21, wherein the hydrogenation is performedat a hydrogen to acetaldehyde mole ratio greater than 2:1.
 27. Theprocess of claim 21, wherein the conversion of the acetaldehyde in thefeed stream is at least 75% and the conversion of the acetic acid in thefeed stream is at least 10%.
 28. The process of claim 21, wherein theethanol mixture comprises from 50 wt. % to 97 wt. % ethanol; from 0.1wt. % to 25 wt. % water; less than 35 wt. % acetic acid; and less than10 wt. % acetaldehyde.
 29. The process of claim 21, further comprisingpurifying the ethanol mixture in one or more separation units to produceethanol.
 30. The process of claim 21, wherein the first metal is presentin an amount of from 0.1 to 25 wt. %, based on the total weight of thecatalyst and is selected from the group consisting of copper, iron,cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium,platinum, titanium, zinc, chromium, rhenium, molybdenum, and tungsten.31. The process of claim 21, wherein the at least one support modifieris present in an amount of 0.1 wt. % to 50 wt. %, based on the totalweight of the catalyst and is selected from the group consisting of (i)alkaline earth metal oxides, (ii) alkali metal oxides, (iii) alkalineearth metal metasilicates, (iv) alkali metal metasilicates, (v) GroupIIB metal oxides, (vi) Group IIB metal metasilicates, (vii) Group IIIBmetal oxides, (viii) Group IIIB metal metasilicates, and mixturesthereof.
 32. The process of claim 21, wherein the support is present inan amount of 25 wt. % to 99 wt. %, based on the total weight of thecatalyst and is selected from the group consisting of silica,silica/alumina, calcium metasilicate, pyrogenic silica, high puritysilica and mixtures thereof.
 33. The process of claim 21, wherein thecatalyst further comprises a second metal different from the firstmetal, wherein the second metal is present in an amount of from 0.1 to10 wt. %, based on the total weight of the catalyst and is selected fromthe group consisting of copper, molybdenum, tin, chromium, iron, cobalt,vanadium, tungsten, palladium, platinum, lanthanum, cerium, manganese,ruthenium, rhenium, gold, and nickel.